It flows through the Liberec and Central Bohemian regions.

[1] The Mohelka originates in the territory of Jablonec nad Nisou in the Jizera Mountains at an elevation of 608 m (1,995 ft) and flows to Mohelnice nad Jizerou, where it enters the Jizera River at an elevation of 220 m (720 ft).

Its drainage basin has an area of 176.5 km2 (68.1 sq mi).

[3] The longest tributaries of the Mohelka are:[4] The river flows through the municipal territories of Jablonec nad Nisou, Pulečný, Rychnov u Jablonce nad Nisou, Rádlo, Hodkovice nad Mohelkou, Žďárek, Paceřice, Sychrov, Radimovice, Vlastibořice, Bílá, Český Dub, Všelibice, Kobyly, Chocnějovice and Mohelnice nad Jizerou.

About 15 km (9 mi) on the lower course of the river is navigable all year round.